Cortland Repertory Theatre's production of "A Murder Is Announced" gives a good idea of why Agatha Christie is such a popular story-teller.

The stage lights come up on a spacious, bright and very comfortable-looking drawing room. Life there surely must be secure, sane and predictable.

Yet within a minute or two a gnawing discomfort takes hold of the half-dozen or more well-dressed people who drift into the room: an ad in the daily newspaper has announced that a murder will take place in that very house, at 6:30 that very evening.

Still, no one gets terribly worried -- "Things like that don't happen here," they agree.

Leslie Darbon's script (adapted from a Christie novel) keeps things cool and comic, British fashion, and they all fall to chatting, sometimes cuttingly, about trivia like clothes and birthdays.

Letitia (Mary Williams), the poised and thoughtful head of the house, asks the foreign-born servant Mitzi (played with riveting and often comic intensity by Renee Reinecke) to make her special goulash recipe for lunch.

"Not too much garlic," says Letitia. Instantly Mitzi's hackles are up: "You don't like garlic?" -- more as an accusation than a question. The stuff of light comedy.

But you trust Christie enough to expect that when the drawing room clock reaches 6:30 p.m., all hell will break loose in this puddle of complacency. It surely does, and it is delivered with maximum punch in this production directed by Jim Bumgardner.

When the mystery is finally unraveled, the thread will turn out to be intricate and ingenious, as is usual with Christie. (To be honest, I got lost at the first mention of "third cousins.")

I don't want to give away too much about the story, but a few features in "A Murder Is Announced" run counter to the standard Christie method.

Unlike recent television "Marples," in this play Miss Marple does not dominate any of the early scenes and has no long speeches until she confronts the killer.

As skilfully played by Carol Burns, Miss Marple is a quiet, friendly lady who makes her few words count, and whose wide-open eyes see everything. She doesn't nose around or inquire; she just absorbs everything, mastering the twists that lead to the guilty party.

Second, this Miss Marple does not bring all the suspects together in one room for the unraveling. She simply assembles her evidence and confronts the murderer.

Third, Inspector Craddock (superbly played by Kyle Kennedy) is not a fumbling functionary. He is a portly, well-dressed man with a diplomatic air and a driving intelligence that makes him a powerful collaborator with Miss Marple.

Christie's strong suit is bringing together a number of sharply defined, sometimes cartoonish characters, all of whom may be concealing deep secrets, and any of whom at a given moment may behave suspiciously.

That gives actors the challenge of making the characters believable and ambiguous, and this cast does that splendidly. And it gives audiences an interesting parade of unpredictable interactions.

I think too that one of Christie's great appeals is the almost philosophical sense that all the stories the characters tell about themselves may be a facade. Now you see it, now it crumbles. All her mysteries depend on the dismantling of various convincing alibis.

Like many other British creative artists, e.g. Gilbert and Sullivan, George Bernard Shaw, Christie habitually presents the social facades that people concoct -- in Christie's case, by the hundreds. Then she has the fun of energetically tearing them down (via her fictional detectives) until the truth emerges, sometimes noble but more often embarrassing.

Meanwhile, all the characters -- usually excepting victims and police -- are suspects.

In "A Murder Is Announced," for example, there's Julia Simmons (Jennifer Holcombe), with a trim figure, long chestnut hair and a habitually sour expression. She never wears the same outfit twice, and she is aware how smashingly good she looks in all of them.

Dora Bunner (Rebecca McGraw, in a beautiful piece of character acting) is an aged lady, a warm, funny ditz, but we really don't know much about her.

And so it goes, through half a dozen other characters.

Jimmy Johnsmeyer's costumes wonderfully reflect the early 1950s, as does sound designer David Huber's pre-show music. Jared Rutherford designed the sweeping but comfortable-looking set, warmly lit by Shawn Boyle.